St-Julians-Computer-Science - 1.1 The Systems Life Cycle

1.1.1 Outline the systems life cycle in terms of the stages: analysis, design, implementation, operation and maintenance

The systems life cycle consists of four main stages, these being analysis, design, implementation, operation and maintenance

Analysis
It is in this section that you attempt to find out how the current system works, what it is used for and how it could

be improved.To do this, you would commonly:

Read instruction manuals
Observe the current system in place being used
Use questionnaires to find out specific answers
Conduct interviews

You would, with this, attempt to find out the feasibility of the system in financial terms, you would find out the advantages and disadvantages of the current system, and you would attempt to find out if an implementation would be possible.

Design

Here you will attempt to set specific system requirements and design the actual system to be put in place. You would need to:

Select the appropriate Hardware, Software and Operating System
Design the user interface
Determine the file structure
Design data validation techniques
Create security procedures (e.g. Passwords)
Design future test plans

Implementation

Implementation can consist of three substages. These are Installation, Testing and Training. There are four basic methods of implementation, these being:

Direct implementation
- The new system is implemented immediately
Phased Implementation
- Parts of the new system are implemented gradually
Pilot Implementation
- The new system is only used in one section of the company
Parallel implementation
- Both systems are run 'side by side'

Operation/Maintenance:

Follows the installation of the system. Even after it is up and running, errors may be found or better ways of doing things may emerge. The potential improvements need to be investigated and analysed, thus starting a new phase of the cycle. Improvements may be identified by periodic reviews of the system, again, perhaps involving the fact finding methods that were used at the original analysis phase. It will be very important that the documentation supplied with the original system is clear and complete. This documentation will be used to make it easier to design modifications to the system.

1.1.2 Explain the importance of collecting data during the analysis stage.

Gathering data is essential in the analysis stage because you can gain clear insight into the problem. If the problem cannot be identified correctly, a poor solution is guaranteed to follow.

1.1.3 Compare the methods of data collection

Method	Advantages	Disadvantages
Interview	Detailed data, can change questions during process (not like questionnaire)	Time-consuming, problems classifying / quantifying data
Questionnaire	Can reach a lot of people, quickly (compared to interview / observation). Numerical analysis possible.	Questions may be mis-interpreted. People may only answer some questions or not respond at all.
Document Search	The data required for the system can be identified accurately.	Documents may be lacking, out-of-date, etc. (interview could discover this)
Literature Search	Can find descriptions / problems of previous implementations (saves work).	Problem may not be described (in detail). Again, working without experienced users.
Observation	Observations are independent of user bias (unlike interview / questionnaire).	Time consuming and observer can affect process: Hawthorne Effect.

1.1.4 Describe the production of a requirements specification during the analysis stage

A requirement specification contains what the system will be able to do and how it will be done. This should include:

The costs of building, testing and running the system (including both hardware and software)
Estimated time till completion
List of hardware/software tools needed
Description of hardware and software functions
Performance of the system
List of personnel and allocated tasks

1.1.5 Outline the features of a feasibility report

A feasibility report can be produced during the analysis, design stage, or both. It should include:

Cost
Expected benefits
Time period
Potential difficulties

The objective of a feasibility report is to identify the costs and estimate expected benefits. It is on the basis of this report that a decision will be taken as to whether to proceed to detailed design or not.

1.1.6 Compare the advantages and disadvantages of alternative solutions in the design stage. This should include both hardware and software solutions

There are a number of different ways a problem can be solved, with or without using a computer. One consideration you must take into account is the input and output of the solutions. The software itself could be one of three types:

General Application Software - This is the least expensive solution but may not include all the features that the user requires. A typical example would be an office package.
Specific Applications Packages - These are typically more expensive then general application software and provide a greater number of features. These programs tend to have been written specifically for business.
Tailor Made Software - This is the most expensive option but can be customized to do exactly what the customer requires as it is written from scratch.

1.1.7 Discuss methods of testing systems, the importance of proper testing and the implications of inadequate testing.

Systems usually go through several stages

of testing. Alpha testing is the first stage in which a small group of qualified individuals examine an early version of the program. Beta testing is when the program is fully featured and released to a wider audience for testing.

Test data is also used to make sure the program outputs the expected data. We can test the program with:

Normal Data - Data that is expected to be entered into the program. Including data at the limits of what is expected.
Extreme Data - This will be outside the normal limits of the program, simulating what happens if a user enters incorrect data by mistake.
Abnormal Data - Data that is not expected, for example a string instead of an integer value.

1.1.8 Outline methods of implementing new systems.

A new system can be implemented in one of the following three ways:

Parallel Running - This is when both new and old systems are run together. This confirms that they both produce the same outputs and if any faults occur they can be fixed with no up-time lost. Staff can be trained without fear of losing data, yet there may be twice as much work to do.
Phased - Parts of the system are implemented at different times, each part is then tested and confirmed, this means it will take much longer to implement.
Direct Changeover - Also know as a "Big Bang" the old system is immediately replaced by the new one. Users need to be trained before the new system is implemented and there is a risk that it will not work correctly.
Pilot Implementation - The new system is only used in one section of the company

1.1.9 Outline the features and importance of maintaining systems.

Proper maintenance of a system is essential. Clear documentation, to begin with, helps this progress as programmers will not need to work hard to understand design decision if they are explained in documentation. This reduces the cost of maintanence. Periodic reviews and performance reviews use the same data collection techniques as seen in the analysis sections and indicate whether further improvements or modifications are needed.

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